Processes for extracting numerous compounds from organic materials, particularly from plants, using supercritical fluid extraction (SFE) are known. Generally, above a critical temperature (T.sub.c) and pressure (P.sub.c), a vapor and a liquid of the same substance have the same density; in this state the fluid cannot be liquified by further increasing the pressure. A supercritical fluid state results when the substance is maintained at its T.sub.c and P.sub.c whereby a transition from gas/liquid to supercritical liquid occurs. For example, a description of the phase changes in a gas (CO.sub.2) and the conditions at which the gas becomes a supercritical fluid (SCF) is known, as described in U.S. Pat. No. 4,749,522.
U.S. Pat. No. 3,899,398 to Cole et al. teaches a process for treating citrus wastes to obtain essential oils by cooking the citrus wastes in the aqueous phase under autogeneous pressure at a temperature of about 350.degree. C. to 750.degree. C., in the absence of air or oxygen.
U.S. Pat. No. 4,749,522 to Kamarei discloses supercritical fluid extraction of animal derived materials and provides generalized teachings that numerous methods can be used to prepared non-dried animal tissues used in the supercritical extraction process, including grinding, crushing, cumminuting, high and low pressure pressing, cryogrinding, flaking, sonication, freezing, freeze-thaw treatment, freeze drying, emulsification, homogenization, filtration, high speed mixing, centrifugation, cell separation, mechanical separation, thermal treatment, and other physical treatment such as treatment with inorganic and organic acids, bases, solvents, surface active agents, colorants, ionization radiation treatment; enzymatic treatment such as endogenous and/or exogenous enzymatic treatment, and any combination of more than one of the above methods of treating the sample. However, in none of his examples does Kamarei teach using treatment with acids of any kind. Nor does Kamarei suggest the use of his process for treating plant materials.
U.S. Pat. No. 4,824,570 discloses a process for supercritical extraction of essential oils from plants with carbon dioxide for preparing pharmaceutical products.
Bonnie A. Charpentier and Michael R. Sevenants (eds.), Supercritical Fluid Extraction and Chromatography, Techniques and Applications, ACS Symposium Series 366, American Chemical Society, Washington, D.C. (1988) discloses, for example, the ultrasonic supercritical fluid extraction (sfe) of caffeine from roasted coffee beans, of omega-3 fatty acids from fish oil and of terpenes from orange essential oil. Carpentier and Sevenants also discloses in Chapter 7, steps to developing a commercial supercritical carbon dioxide processing plant, and teaches that most solvent extraction using CO.sub.2 are run at temperatures between 10.degree. C. and 50.degree. C., mild temperatures which are not likely to degrade or volatize heat-sensitive aroma compounds. The authors further teach that some materials may require pre-treatment processing (i.e. physical methods) to prepare the material for extraction or post-treatment of the residue after extraction is completed, further stating that materials handling systems such as conveyors and product silos must be designed with these considerations in mind.
Bioprocessing Technology, a monthly intelligence service from Technical Insights, Inc., Vol. 11, Number 11, November 1988 discloses that supercritical fluids, using as its solvent carbon dioxide, can be used to isolate diosgenin, a building block for sterols from plant cell culture.
J. M. Wong and K. P. Johnston, Biotechnology Progress, Vol. 2, No. 1, March 1986, pp. 29-39 teach the solubilization of biomolecules, such as sterols, in carbon dioxide based supercritical fluids.
L. Sanchez et al., Analyst (London) 97 (1161) pp. 973-6 (Chem. Abstract 78(13):81734c) teach that crude diosgenin was obtained from barbasco root by hydrolysis with 30% HCl followed by extraction with CHCl.sub.3.
None of these references teach supercritical fluid extraction of compounds from plant materials which were hydrolyzed either prior to or during contacting with a supercritical fluid.